1. FIELD OF THE INVENTION
The present invention relates to a travel path displaying apparatus in which a current location and a path of travel of a running body, such as an automobile, are displayed on a display screen which has a map previously displayed thereon.
2. DESCRIPTION OF THE PRIOR ART
In an attempt to prevent a driver of an automobile or the like from losing his way in driving, for example in a strange place, from his desired travel path, there has been developed a travel path displaying apparatus including a distance detector for detecting a distance of travel of a running body and a direction detector for detecting a running direction wherein the current location of the running body on two-dimensional coordinates is successively computed from the respective results of the above-mentioned detections and the location thus computed is displayed on a display screen having a map having azimuthal coordinates corresponding to said two-dimensional coordinates.
In such travel path displaying apparatus, in which the direction detector includes a geomagnetism sensor, a declination .DELTA..theta., as shown in FIG. 4, is caused between an azimuth detected by the geomagnetism sensor (as indicated by a broken line in FIG. 4) and an azimuth on the map (as indicated by a solid line in FIG. 4), depending upon a particular area. In Japan, the declination .DELTA..theta. is 6.degree.-10.degree. and in a particular point in the world the declination .DELTA..theta. may be several tens of degrees. Accordingly, it is necessary to effect an correction of the declination in running direction of the running body detected by the geomagnetism sensor.
Heretofore, it has been a practice to previously determine declination data with respect to a particular map of the relating area which is used to display the travel path, and to effect a arithmetic operation to correct the declination in running direction of the running body, which has been detected by the geomagnetism sensor, by means of a signal processing device.
However, it requires a very troublesome step to previously register declination data with respect to every map of a plurality of areas and to read out the proper declination data concerning a desired area, depending upon the map which is to be used in the display of the travel path.